全文获取类型
收费全文 | 27852篇 |
免费 | 3965篇 |
国内免费 | 5066篇 |
专业分类
测绘学 | 1223篇 |
大气科学 | 4711篇 |
地球物理 | 6834篇 |
地质学 | 13042篇 |
海洋学 | 2957篇 |
天文学 | 2698篇 |
综合类 | 2447篇 |
自然地理 | 2971篇 |
出版年
2024年 | 68篇 |
2023年 | 338篇 |
2022年 | 917篇 |
2021年 | 1065篇 |
2020年 | 908篇 |
2019年 | 1036篇 |
2018年 | 1376篇 |
2017年 | 1223篇 |
2016年 | 1478篇 |
2015年 | 1077篇 |
2014年 | 1444篇 |
2013年 | 1596篇 |
2012年 | 1345篇 |
2011年 | 1574篇 |
2010年 | 1385篇 |
2009年 | 1553篇 |
2008年 | 1340篇 |
2007年 | 1279篇 |
2006年 | 1083篇 |
2005年 | 1107篇 |
2004年 | 846篇 |
2003年 | 873篇 |
2002年 | 831篇 |
2001年 | 776篇 |
2000年 | 865篇 |
1999年 | 1170篇 |
1998年 | 966篇 |
1997年 | 1031篇 |
1996年 | 963篇 |
1995年 | 815篇 |
1994年 | 673篇 |
1993年 | 597篇 |
1992年 | 466篇 |
1991年 | 370篇 |
1990年 | 303篇 |
1989年 | 257篇 |
1988年 | 233篇 |
1987年 | 224篇 |
1986年 | 167篇 |
1985年 | 134篇 |
1984年 | 117篇 |
1983年 | 114篇 |
1982年 | 108篇 |
1981年 | 95篇 |
1980年 | 88篇 |
1979年 | 78篇 |
1977年 | 59篇 |
1976年 | 58篇 |
1975年 | 48篇 |
1973年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The large-scale structure associated with the 2′N HNCO peak in Sgr B2 [Minh, Y.C., Haikala, L., Hjalmarson, Å., Irvine, W.M., 1998. ApJ 498, 261 (Paper I)] has been investigated. A ring-like morphology of the HNCO emission has been found; this structure may be colliding with the Principal Cloud of Sgr B2. This “HNCO Ring” appears to be centered at (l,b) = (0.7°,−0.07°), with a radius of 5 pc and a total mass of 1.0 × 105 to 1.6 × 106 M. The expansion velocity of the Ring is estimated to be 30–40 km s−1, which gives an expansion time scale of 1.5 × 105 year. The morphology suggests that collision between the Ring and the Principal Cloud may be triggering the massive star formation in the Sgr B2 cloud sequentially, with the latest star formation taking place at the 2′N position. The chemistry related to HNCO is not certain yet, but if it forms mainly via reaction with the evaporated OCN− from icy grain mantles, the observed enhancement of the HNCO abundance can be understood as resulting from shocks associated with the collision between the Principal Cloud and the expanding HNCO Ring. 相似文献
32.
33.
This paper proposes a multi‐level parallelized substructuring–frontal combined algorithm for the analysis of the problem of thermo/hydraulic/mechanical behaviour of unsaturated soil. Temperature, displacement, pore water pressure and pore air pressure are treated as the primary variables in a non‐linear analysis. Details are given firstly of the substructuring–frontal combined approach. The incorporation of the algorithm in a multi‐level parallel strategy is then discussed. The parallel processing can thus be carried out at different substructural levels. The method thus developed impacts, in a positive way, on both computer storage requirement and execution time. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
34.
The dunes in estuary of Tumen River in China lie to the area between the Jiushaping and Fangchuan in the left bank of Tumen River (Fig.1). The dis-tance is about 15~20 km between the dunes and the coast. It ranges from China to D. P. R. Korea and Russia. The range of the height of dunes is about 15~20 m and the width is 100~200 m. By the re-connaissance, we protracted 9 section planes of the dunes and collected 40 sand samples of the dunes, and identified the sedimentary environment … 相似文献
35.
Hong-Qi Zhang Xing-Ming Bao Yin Zhang Ji-Hong Liu Shu-Dong Bao Yuan-Yong Deng Wei Li Jie Chen Jin-Ping Dun Jiang-Tao Su Juan Guo Xiao-Fan Wang Ke-Liang Hu Gang-Hua Lin Dong-Guang WangNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(6):491-494
We analyze the magnetic configurations of three super active regions, NOAA 10484, 10486 and 10488, observed by the Huairou Multi-Channel Solar Telescope (MCST) from 2003 October 18 to November 4. Many energetic phenomena, such as flares (including a X-28 flare) and coronal mass ejections (CMEs), occurred during this period. We think that strong shear and fast emergence of magnetic flux are the main causes of these events. The question is also of great interest why these dramatic eruptions occurred so close together in the descending phase of the solar cycle. 相似文献
36.
The most general accurate solutions for the Buchdhal fluid sphere were obtained and matched with the Schwarzchild's exterior
solution at the pressure free interface. Various parameters of the solutions were so adjusted that the energy density, pressure
and temperature were positive and decreasing away from the centre, and the velocity of sound was less than unity throughout
the spheroid model. Using this procedure, the maximum mass of the fluid sphere with a surface density of2 × 1014gm cm-3 was determined to be 3.82MΘ and 4.57 MΘ for strong and weak energy conditions respectively. PACS number: 0402, 0402J, 0440D,
95301
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
37.
38.
J.-M. Carquillat N. Ginestet J.-L. Prieur Y. Debernardi 《Monthly notices of the Royal Astronomical Society》2003,346(2):555-564
We present the results of a radial-velocity study of eight Am stars (HD 341, 55822, 61250, 67317, 93991, 162950, 224890 and 225137) observed at Observatoire de Haute-Provence with the CORAVEL instrument. We find that these systems are single-line spectroscopic binaries whose orbital elements are determined for the first time. 相似文献
39.
论社会共同价值观 总被引:1,自引:0,他引:1
刘正球 《广东海洋大学学报》2003,23(2):49-56
社会共同价值观是社会共同体之所以能存在和发展的凝聚力、它指导社会共同体及其成员的前进方向、它还规范和约束社会共同体成员的思想和行动以形成社会共同体的合力。社会共同价值观是在一定历史时期的特定社会共同体中各社会阶层的社会成员普遍认同并持有的价值观。社会共同价值观具有普遍性、结构性、稳定性等特征 ,具有凝聚功能、导向功能和规约功能。社会共同价值观具有理论体系的形式、文化形式、社会心理的形式等存在形式 相似文献
40.
茅排金矿床属中-低温硫化物金矿床,矿体的分布严格受断裂构造控制.通过应用不同的物探方法来寻找控矿断裂,从而达到间接地寻找矿体分布的目的,取得了较好的效果。 相似文献